444 OUTLINES OF CHORDATE DEVELOPMENT 



FIG. 182. Diagrammatic section through the gravid human uterus and the 

 embryo at the seventh or eighth week. From Quain's Anatomy, after Allen 

 Thomson, al, Allantois; am, amnion; c, c, openings of the oviducts (Fallopian 

 tubes) into the uterine cavity; c', cervix filled with mucous plug (the reference 

 letters c,c,c', are placed in the cavity of the uterus; ch, chorion with vascular 

 villi growing into the decidua capsularis and decidua basalis; in the decidua cap- 

 sularis the villi are becoming atrophied (chorion Iseve) ; dr, decidua capsularis; 

 ds, decidua basalis; dv, decidua vera; i, embryo; u, umbilical cord; y, yolk-sac; 

 y r , yolk-stalk; 



